Schorl


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schorl

[shȯrl]
(mineralogy)

Schorl

 

a mineral, a black ferruginous variety of tourmaline with isomorphic admixtures of magnesium, manganese, and trivalent iron (seeTOURMALINE). Schorl is found in granites, pegmatites, greisens, skarns, gneisses, hydrothermal veins, and various metamorphic shales.

References in periodicals archive ?
K-type pegmatites contain K-feldspars (microcline), muscovite and/or biotite, tourmalines (generally only black schorl), beryl (almost solely aquamarine), and almandine.
Struverite occurs there in a medium-grained pegmatite, in association with rare beryl, schorl and almandine.
Because the mined portion of this pegmatite is also weathered, most specimens are very fragile and the crystals are mostly loose, but there have also been some good-quality specimens on matrix mined, some of them containing schorl in association.
Isaias's specimens are miniatures--from about 4 to about 7 cm across--showing lustrous, transparent, entirely colorless prismatic crystals, to 3 cm, of goshenite beryl perching lightly on sleek black schorl crystals; some specimens harbor tiny colorless topaz crystals as well.
Black schorl, Na[([Fe.sup.2+])sub.3][Al.sub.6][([BO.sub.3]).sub.3][[Si.sub.6][O.sub.18]][(OH).sub.4], is also abundant, as single crystals and clusters measuring up to 30 cm, on quartz, albite and microcline crystals.
Schorl on Quartz Shigar Valley, Skardu, Pakistan 5 1/2" tall
Only lustrous terminated schorl crystals in kaolinized pegmatite and holmquistite in pegmatite contact schists have been abundant enough to be found in many collections.
Minerals have been collected in the Erongo Mountains of Namibia for nearly 90 years, culminating in the 1999 discovery of some of the finest Namibian aquamarine, schorl and jeremejevite ever seen.
From 1999 to 2006, some of the finest Namibian aquamarine, schorl and jeremejevite ever seen were collected in the Erongo Mountains, together with aesthetic fluorite, quartz, goethite pseudomorphs after siderite, and other important species such as cassiterite, ferberite and metazeunerite.
For example, the Desmond Sacco collection has a large half-"bowtie" schorl acquired in the late 1960's; the Natural History Museum in London has a plumbogummite from Krantzberg, purchased from well-known collector-dealer Charles Key in 1985; and one of us (BC) has a thumbnail schorl on granite matrix purchased in 1981 from Carlton Gems & Minerals in Johannesburg.
Even more beautiful were some miniature specimens of almandine-spessartine on schorl, both species performing brilliantly: the garnets are flashing, deep red, part-gemmy trapezohedrons to 2.5 cm, and the schorl crystals on whose prism faces they rest are bright black (however, one or both ends of most of the schorls are broken off).